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Topic: HE_AAC_V2 encoder ignored much sound (Read 9765 times) previous topic - next topic
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HE_AAC_V2 encoder ignored much sound

Hi all,

I'm trying encoding some of my audio files into low bitrate (24kpbs) streams. I found HE_AAC_V2 as the best option.

Suprisingly, encoding one audio file (wmav2 format) containing conversation produces an silent audio file. I've tried neroaacenc, winamppro on Windows and ffmpeg with libaacplus, ffmpeg with libfdk_aac, Max and XLD on Mac.

Then I used Audacity to mix this audio file with another audio file into one audio file. This second audio file can be properly encoded by HE_AAC_V2. Next I encoded this mixed file into m4a with HE_AAC_V2 and I'm astonished to find out that sound from the first audio file does not exist in the resulting file while sound from the second file is OK.

Command line I used is as follows:

ffmpeg -i <input_file> -vn -sn -c:a libfdk_aac -profile:a aac_he_v2 -ar:a 44100 -ac:a 2 -b:a 24k -f adts <output_file>
ffmpeg -i <input_file> -vn -sn -c:a libaacplus -ar:a 44100 -ac:a 2 -b:a 24k -f adts <output_file>

What does this mean? Some sound cannot be encoded by it?

HE_AAC_V2 encoder ignored much sound

Reply #1 –
It might not be an encoder problem. The file might not be able to decoded properly.
Try:
ffmpeg -i <input_file> -c:a pcm_s16le -ar:a 44100 -ac:a 2 output_file.wav
Can you playback output_file.wav? If not then ffmpeg was unable to decode the audio correctly.

HE_AAC_V2 encoder ignored much sound

Reply #2 –
Thanks for your quick replay but
Yes, it can

HE_AAC_V2 encoder ignored much sound

Reply #3 –
Coppla, can you upload a part of the wma2 file which is encoded as silence in the upload forum? HE-AACv2 might have problems with out-of-phase files.

Chris
If I don't reply to your reply, it means I agree with you.

HE_AAC_V2 encoder ignored much sound

Reply #4 –
Hi Helmrich,

I've just registered and I cannot find the way to upload attachments.

HE_AAC_V2 encoder ignored much sound

Reply #5 –
Try playing output_file.wav in mono. My guess is that you will hear silence.

HE AAC V2 files contain mono data with information to direct the output toward one channel or the other. Out-of-phase audio will simply cancel.

HE_AAC_V2 encoder ignored much sound

Reply #8 –
Quote from: pdq on
Try playing output_file.wav in mono. My guess is that you will hear silence.

HE AAC V2 files contain mono data with information to direct the output toward one channel or the other. Out-of-phase audio will simply cancel.


Hi pdq,

You're right. I used Audacity to mix the two channels into one channel and the resulting waveform is a straight line...
What can I do to this audio file to correctly encode it into HE AAC V2?

HE_AAC_V2 encoder ignored much sound

Reply #9 –
Quote from: coppla on
What can I do to this audio file to correctly encode it into HE AAC V2?

With Audacity:

Click on the drop down menu at the top of the properties box of the sound, on the left
Split stereo track
Select right channel sound
Effect -> Invert
Drop down menu at the top of the properties box -> Make Stereo Track
Save the resulting sound
Done.

HE_AAC_V2 encoder ignored much sound

Reply #10 –
Quote from: Brazil2 on
Quote from: coppla on
What can I do to this audio file to correctly encode it into HE AAC V2?

With Audacity:

Click on the drop down menu at the top of the properties box of the sound, on the left
Split stereo track
Select right channel sound
Effect -> Invert
Drop down menu at the top of the properties box -> Make Stereo Track
Save the resulting sound
Done.


Thank you, it works.

BTW, I'm still wondering if i can invert channel with ffmpeg